Inner-diameter enlargement of multi-walled carbon nanotubes by adding HBO3 in catalyst

Multi-walled carbon nanotubes (MWCNTs) with large inner diameter were synthesized by the catalytic chemical vapor deposition method using HBO3 as the accessorial catalyst in reaction precursors. A ratio D-in/D-out is defined as an index to evaluate the hollow degree of MWCNTs, where D-in and D-out are the inner and outer diameter of one CNT, respectively. When no HBO3 was added in the reaction mixtures, the MWCNTs are straight with thick wall. The average D-in/D-out value is only 0.08+/-02. The X-ray diffraction (XRD) result shows the relatively low crystallinity. When HBO3 was added in the reaction precursors, the MWCNTs have large inner cavity and the average D-in/D-out value reaches 0.57+/-0.10. The crystallinity was also improved remarkably. These results indicate that HBO3 in the catalyst system has great influence on the growth of MWCNTs. (C) 2011 Elsevier B.V. All rights reserved.